Many devices in today's market include elements which must be replaced or maintained periodically in order to provide optimal efficiency. Some of these devices have two separate and distinct elements that may be replaced at different timed intervals or timed periods. Furthermore, even in cases wherein two elements should be replaced at the same time, in actual use, they oftentimes are replaced at different times due to the other factors such as the lack of replacement elements, personnel schedules or the like. In such event, the actual replacement sequence of these two elements may become different, and thus a dual indicator may be desired to indicate the actual replacement time or schedule of each element.
By way of example, air purifiers have grown in popularity in recent years. A growing concern for health and an increased recognition of the risks associated with unclean air are largely responsible for this trend. For example, airborne pollutants can cause or contribute to a number of respiratory problems, including respiratory infections, asthma, and allergies. Additionally, some airborne pollutants can cause undesirable odors. While air purifiers are available in a wide variety of designs, a conventional air purifier includes a blower that moves air through a filter element. A number of different filter elements with different filtering characteristics are commercially available. For example, particulate filters are available to remove particulate matter from air. A conventional particulate filter includes a substance, such as fiberglass or electret-type media, that traps particulate matter as air is passed therethrough. Another example, odor filters are available to remove odors from the air. A conventional odor filter includes activated carbon, or activated charcoal, which removes pollutants from the air primarily by absorption. Another form of a filter may include two filter elements of varying filtering capabilities. A pre-filter may be used remove large particulates from the air while a subsequent filter in the air flow removes finer or smaller particulates. As the pre-filter and fine particulate filter may have different useful lives it would be desirous for the air purifier to include an indicator to show the scheduled replacement date for each of the two filters. However, because of limited space available on the face of an air-purifier it may not be able to accommodate multiple indicators.
Accordingly, it is seen that a need remains for a schedule indicator that can indicate two separate timing intervals without occupying a large amount of space. It is to the provision of such therefore that the present invention is primarily directed.